The present invention relates to a zoom lens and an image pickup device, for example, a zoom lens system used for an optical unit for taking in an image of a photographic object with an image pickup sensor and an image pickup device (especially, an image pickup device which is a main structural element of a camera which is installed inside or outside of a digital camera, a personal computer, a mobile computer, a mobile phone, an information mobile terminal, etc.) equipped with it.
In recent years, a digital camera spreads quickly, and is used not only as a means taking an image into a computer, but also used widely as a means for leaving behind photographs as same as a conventional silver halide film camera. Further, the miniaturization of a camera unit also has progressed with the miniaturization of an image pickup sensor, and a micro camera unit has mounted commonly on a mobile phone. In addition to an object to leave behind photographs, adaptation for a trend to increase the number of pixels and an enlargement of a zooming region has been requested strongly as the specification of an image pickup optical system.
As one of the means for satisfying these requests, U.S. Pat. No. 7,085,072B2 and US 2007/0024984A1 has proposed a zoom lens which is designed to be miniaturized with the structure that a first lens group having a positive power, a second lens group having a negative power, a third lens group having a positive power and a fourth lens group having a positive power are arranged in this order from the object side.
The zoom lens proposed in U.S. Pat. No. 7,085,072B2 and US 2007/0024984A1 includes a reflecting surface to bend a light flux by almost 90° in the first lens group and attains changeable magnifications of two times to three times. However, there is a problem that a size of the optical system is relatively large.
The present invention has been conceived in view of the above circumstances, and its object is to provide a zoom lens system which achieves the miniaturization and has a changeable magnification of about three times.